Optical devices such as waveguides, gratings, and switches, for example, are typically fabricated in layers of silica deposited on silicon. One problem that occurs when employing these materials is that strain birefringence arises because of the large thermal expansion coefficient of silicon relative to silica. As a result of this difference in expansion coefficients, large compressive strains are produced in the silica layers after the requisite annealing step is performed during the fabrication process. The resulting birefringence caused by the strains produce different propagation constants for the TE and TM waveguide modes. Because the modes have different propagation constants, an optical signal propagating through a device is split into two components corresponding to the TE and TM modes. The components are characterized by different wavelengths of maximum transmission and the difference, which is referred to as the polarization shift, is typically about 0.3 nm at a wavelength of 1.5 microns. A polarization shift of this magnitude is too large for many applications in which optical devices are employed. For example, frequency routing devices having channel spacings of less than 2 nm are required for long-haul or local area networks. For such purposes the routing device typically should have a polarization shift of less that about 0.1 nm. Accordingly, it is desirable to reduce the polarization shift in optical devices.